The ultimate long term objective of the proposed project is elucidation at the subcellular level of the enzymatic processes involved in the regulation of the flow of high energy phosphate generated by mitochondrial oxidative phosphorylation and its channelling to the specific loci of utilization during the excitation-contraction cycle, a crucial process in normal cardiac function. A detailed investigation will be conducted on the properties of the three major heart isoenzymes of creatine kinase. Specific emphasis will be placed upon their special catalytic function, regulation, subunit structure, amino acid composition, and substrate binding properties. An original contribution of this study will be the exploration of energy-channelling directed by specific microcompartmentation of creatine kinase isoenzymes. Repetitive contraction of heart muscle demands the coordination of four separate energy-dependent events: initiation of contraction by the wave of depolarization, contraction of the myofibrils, relaxation involving calcium segregation, followed by the regeneration of ATP. Information obtained from this research will contribute unique knowledge in two areas of cardiac bioenergetics: (1) the molecular mechanisms by which high-energy phosphate transfer is effected and controlled at the enzymatic level; and (2) how energy is directed from the mitochondrion to specific sites of utilization, i.e. the myofibrils, the sarcoplasmic reticulum, and the cell membrane. Furthermore, together with previous studies on the sequence of isoenzyme release into the serum after acute myocardial infarction the proposed localization experiments will provide novel dynamic insight into the early sequela of cellular necrosis.